Alexander von Humboldt was an important figure in which of these fields of study?

Friedrich Wilhelm Heinrich Alexander von Humboldt (14 September 1769 – 6 May 1859) was a German polymath, geographer, naturalist, explorer, and proponent of Romantic philosophy and science. He was the younger brother of the Prussian minister, philosopher, and linguist Wilhelm von Humboldt (1767–1835).

Humboldt's quantitative work on botanical geography laid the foundation for the field of biogeography. Humboldt's advocacy of long-term systematic geophysical measurement laid the foundation for modern geomagnetic and meteorological monitoring.

Between 1799 and 1804, Humboldt travelled extensively in the Americas, exploring and describing them for the first time from a modern Western scientific point of view. His description of the journey was written up and published in several volumes over 21 years. Humboldt was one of the first people to propose that the lands bordering the Atlantic Ocean were once joined (South America and Africa in particular).